The vestibular system is responsible for collecting information about the head's position and movement in space. This information is used to maintain posture through the actions of the vestibulospinal reflexes and to stabilize gaze by means of the vestibulo-ocular reflex (VOR). Dysfunction of these reflexes due to disruption of vestibular input to the brainstem can lead to pathologies such as Meniere's disease and aminoglycoside toxicity and may bring about disabling vertigo and disequilibrium. In mammals, three types of vestibular-nerve afferent neurons carry these signals from the vestibular periphery to the brainstem, but the purpose for these separate classes is not known. Based on their sensitivity and baseline discharge patterns, they have been termed "regularly discharging," "irregularly discharging," and "low-gain irregularly discharging." Indirect evidence suggests that these afferent types may be differentially affected by various pathologic processes. The studies proposed here aim to define the contribution of irregular afferents to the VOR by reversibly stimulating or inhibiting their contribution to the vestibulo-ocular reflex during high-frequency sinusoidal rotations as well as short transient motions of the head. The dynamics of irregular afferents suggest that their contribution to the VOR may be particularly important under these previously untested conditions. Techniques of signal theory will be used, based on the responses of individual afferents to sharp movements, to determine the relative information carrying capacity of neurons over the short latencies (< 10 ms) allowed by the VOR. A model of vestibular-nerve afferents that predicts neural responses to high-frequency and transient head motion will be developed from the data collected. Findings from this study will allow better understanding of pathologies of the peripheral vestibular system.